Liquid oxygen compatible dye penetrant method for metal defect inspection

ABSTRACT

A liquid fluorescent dye penetrant containing a high volume concentration of a liquid halocarbon is taught as a very sensitive microdefect detector on metal surfaces. The dye penetrant is insensitive to chemical reaction or detonation with liquid oxygen in a standard impact safety test. The liquid dye penetrant safety factor is important in inspection of metal components later fabricated into rocket motor systems, which use liquid oxygen (LOX) in propellant systems, or the like powerful liquid oxidizers.

United States Patent 1 Molina LIQUID OXYGEN COMPATIBLE DYE PENETRANTMETHOD FOR METAL DEFECT INSPECTION [75] lnventor: Orlando G. Molina,Westminster,

Calif.

[73] Assignee: North Americah Rockwell Corporation, El Segundo, Calif.

[22] Filed: Mar. 5, 1970 [21] Appl. No.: 16,803

EXAMPLE it I31 e EXAMPLE 3,561,262 2/1971 Borucki 73/104 3,096,1427/1963 l-Iartmark.... 8/85 3,518,205 6/1970 Vukasovich 252/30133,555,071 1/1971 Rao 260/453 Primary Examiner-Norman G. TorchinAssistant Examiner-John R. Miller AztorneyL. Lee Humphries and Harold H.Card [57] ABSTRACT A liquid fluorescent dye penetrant containing a highvolume concentration of a liquid halocarbon is taught as a verysensitive microdefect detector on metal surfaces. The dye penetrant isinsensitive to chemical reaction or detonation with liquid oxygen in astandard impact safety test. The liquid dye penetrant safety factor isimportant in inspection of metal components later fabricated into rocketmotor systems, which use liquid oxygen (LOX) in propellant. systems, orthe like powerful liquid oxidizers.

6 Claims, 1 Drawing Figure ml A X iAK '1 LIQ UID OXYGEN COMPATIBLE DYEPENETRANT METHOD FOR METAL DEFECT INSPECTION CROSS REFERENCE TO ARELATED APPLICATION This application relates to the copending US. Patentapplication Ser. No. 655,752, filed July 25, 1967, by O. G. M olinawhich was abandoned in favor of a continuation application, Ser. No.68,475 filed Aug. 31, 1970, now abandoned. Further, this applicationrelates to the copending application titled MANUFACTURING A SENSITIVENON-FLAMMABLE DYE PENETRANT Ser. No. 16,806 on Mar. 5, 1970, now US.Pat. No. 3,671,183, by the same inventor, O. G. Molina.

BACKGROUND OF THE INVENTION Dye penetrants are very useful adjuncts fornondestructive testing of metal workpiece surfaces. In many importantand expensive mechanical devices, it is necessary to inspect every metalcomponent of the system for structural defects, prior tofmalfabrication.

Dye penetrants are useful in decreasing inspection processing time andcan be highly sensitive in detecting microdefects in metal components ofaluminum, steel, nickel, titanium and the like. It is particularlydesirable that the inspection system, and the dye penetrants used ininspection, do not increase the danger or sensitivity of the mechanicalcomponents to reaction withstrong oxidizers, which may later be placedin the mechanical devices. For example, a large rocket propellant motorand its propellant tanks may use liquid oxygen (LOX), or a like strongoxidizer, in the rocket propellant. It is quite important that the LOXnot be reactive with any traces of the inspection dye penetrant whichmay remain in the microdefect of the inspected propellant tanks or othercomponents, fabricated from inspected metal stock after cleaning. Theteaching of this invention eliminates the hazard of traces of dyepenetrant reacting explosively with liquid oxygen or other strongoxidizers.

SUMMARY OF THE INVENTION A LOX and gaseous oxygen compatible liquid dyepenetrant is taught, having good sensitivity for detection ofmicro-defects in metal sqrfaces. The liquid dye penetrant has lowproportions of: N-methyl 2- pyrrolidone, isobutyl heptyl ketone, anon-ionic wetting and spreading agent, a fluorescent dye and afluorescent dye brightener, all dissolved in a large proportion of ahalocarbon. The halocarbon is a nonflammable liquid volatile at roomtemperature, relatively nontoxic, resistant to hydrolysis in contactwith water, and inexpensive. The improved modification in dye penetrantis insensitive to chemical reaction, when tested at 72 ft. lb. impact onI/l6 inch thick aluminum discs, covered with the dye penetrantcomposition.

Included in the objects of this invention are:

First, to provide a halocarbon solvent base homogeneous' liquid dyepenetrant which is useful in metal surface micro-defect inspectiontests, and is chemically compatible with LOX service.

Second, to provide a homogeneous halocarbon solvent base dye penetrantwhich is a sensitive detector of microdefects in metal surfaces.

Third, to provide a relatively non-toxic halocarbon solvent base dyepenetrant for detecting microdefects in metal surfaces.

Fourth, to provide a liquid dye penetrant for metal surface microdefectdetection which is not chemically reactive with some common structuralmetals or LOX and gaseous oxygen. 1

Further objects and advantages of this invention will become apparent inthe following description to be read in conjunction with theaccompanying micropho tograph.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a microphotograph of aquenched aluminum test specimen, comparing the sensitivity oninspection, of the dye penetrant of this invention with the sensitivityon inspection of another dye penetrant of the same general chemicalcomposition.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the manufacturing of largethrust rocket motor systems, the functional reliability and the highcost of the motor system necessitate detailed inspection of the systemsmetal components during manufacture. LOX is a common superior oxidizerin rocket liquid propellants. It is important that the standard dyepenetrant inspection technique does not provide organic residues in themicro structure of the inspected metal components which can reactchemically and explosively, with the liquid or gaseous oxygen in ambientcontact with the metal surfaces of the rocket motor system.

This very sensitive homogeneous liquid dye penetrant utilizes as a base,a non-toxic, nonflammable halocarbon, which is volatile at roomtemperature and which does not hydrolyse in the presence of moisture.The halocarbon can be selected from the class listed in Table l. Theother dye penetrant components are selected from N-methyl-Z-pyrrolidone,a ketone, 21 wetting and spreading agent, a fluorescent dye, and a fluorescent dye brightener. Other of the dye penetrant components arepresent in minor volume concentrations, compared to the major volumeconcentration of the halocarbon.

Typically, the LOX compatible, sensitive liquid dye penetrant has thecomposition listed in Example I.

EXAMPLE I Volume Percent N-methyI-Z-pyrrolidone 0.44

lsobutyl heptyl ketone 1.30

Wetting and spreading agent I 2.59

Brightening agent for fluorescent dye H 0.35

Fluorescent dye 0.12

Halocarbon 95.2

Typically, nonionic Tergitol NPX-monyl phenyl polyethylene glycol Q IQJL z z lms "Calcofluor White RW-a fluorescent dye brightenermanufactured under US. Pat. No. 2,920,203, issued January 5, I960.

"* Fluorol 7 GA-Color Index No. equivalent to Fluorescent BrightenerAgent No. of The Colour Index, 2nd Edition, 1956, Published by Societyof Dyers and Colourists and the Am. Assn. Textile Chemists andColorists, London, England and New York, N.Y.

TABLE 1 l-Ialocarbon Solvents BP(F) 3 2-dichloro-2-fluoro ethaneCCl,FCCl,F 199. 4. 1,1,1, trichloro ethane CCI CH, 165. 5.trichloroethylene CHCl=CCl, 188. 6. tetrachloro ethylene CCl,=CCl, 250.

Other examples of the liquid dye penetrant of this invention are listedin the two examples below.

Example II Volume Percent N-methyl-2-pyrrolidone 0.94 lsobutyl heptylketone 2.82 Brightening agent for fluoroescent dye 0.75 Fluoroescent dye0.25 Trichloroethane 95.2 See Example I footnote See Example I footnoteEXAMPLE III Volume Percent N-methyl-2-pyrrolidone 0.46 Isobutyl heptylketone 1.41 Wetting and spreading agent 0.94 Wetting and spreading agent1.41 Brightening agent for fluorescent dye 0.37 Fluorescent dy 0.12Trichloroethane 95.3 *See Example I footnote "See Example l footnote"*See Example 1 footnote "*"Typically nonionic Tergitol NP-l4-nonylphenyl polyethylene glycol C,H|,C,M4O (CH,CH,O), H

In the teaching of this invention the halocarbons listed in Table l arefully equivalent in use in Examples 1, II and III. Other nonionicwetting and spreading agents, such as trimethylnonanol polyethyleneglycol and octyl phenoxyethanol, and the like can be utilized. Otherequivalent ketones can be utilized, such as acetone, b.p. 56C;methylamyl ketone, b.p. 152C; ethyl butyl ketone, 147C; ethyl heptylketone, b.p. 211C;

and the like. Other fluorescent dyes than the Fluorol 7 GA of Example Ican be usedfand other fluorescent brightening agents.

It is required that all components of the dye penetrant composition bemutually soluble within the taught dye penetrant composition volumeconcentration ranges. Within the scope of this invention the volumeconcentrations of the N-methyl-Z-pyrrolidone, fluorescent dye, and ofthe brightening agent for the fluorescent dye each need not exceed onevolume percent. The ketone component and the wetting and spreading agenteach do not exceed five volume percent. The halocarbon solvent ormixture of halocarbon solvents comprise the balance of the composition.

The scope of the teaching of this invention is illustrated by thecomparative impact tests measurements which determine the compatibilityof the dye penetrant compostions with liquid oxygen, and by thecomparative microphotographs of FIG. 1.

In National Aeronautics and Space Administration specificationMSFC-SPEC-IO6A, dated May 5, 1964, criteria and a method wereestablished for determining the compatibility and impactsensitivity ofmaterials with liquid and gaseous oxygen. Using the liquid dye penetrantcompositions disclosed in Examples 1, II and III, impact sensitivitytests were conducted. Individual, clean, unsealed, sulfuric acidanodized aluminum 606l-T6 discs, 1 1/16 inch diameter by 0.063 inchthick, were vapor degreased, then respectively soaked in the liquid dyepenetrant of Examples I, II and III. The discs were then drained, at a90 angle, for minutes, and tested in an impact tester of conventionaltype, de-

character to the earlier examples was also impact; tested as detailedabove. The composition of this comparative penetrant is listed inExample IV below.

EXAMPLE IV Volume Percent N-methyl-Z-pyrrolidone 9.98 Isobutyl heptylketone 29.8 Wetting and spreading agent 19.8 Wetting and spreading agent29.8 Brightening agent for fluorescent dye 7.98 2.64

Fluorescent dye *See Example I footnote See Example I" footnote SeeExample I footnote *"See Example I footnote All of the dye penetrantExamples I, II and Ill successfully passed the 72 ft lb impact testswith LOX, as listed in Table 2. The dye penetrant of Example IV did notpass the same impact test, failing 15 times, out of 20 tests.

Having established theL'OX compatibility of Examples I, II and III,their comparative sensitivity in detecting microdefects is wellillustrated in the microphotographs of FIG. 1. A standard thermallytreated microdefect sensitivity test block of 2014 aluminum is preparedby a water quench. A groove is disposed across the specimen blockseparating two equal block areas for test comparison purposes. The

TABLE 2 Oxygen Impact Tests Penetrant No. Reactions Example Total No.Tests Example 1 0/20 Example ll 0/20 Example III 0/20 Example IV 15/20microcracks are uniformly distributed over the two test areas of theblock, varying in length. In accordance with standard shop practice, twoseparate examples of dye penetrants are each separately painted on theseparate test block areas, the excess of each solution washed off thetest block with a water spray, and then dried with an air blast.Inspection of the comparative optical intensity of the penetrant treatedmicrodefect or crack structure, at low power magnification, underultraviolet light, clearly displays the microdefect structure. Detailedinspection tests have shown that the Examples I, II and III compositionsare clearly equivalent to the much more concentrated composition ExampleIV in the clarity and detail of the optical display of the microcrackstructure. FIG. 1 illustrates the compara' tive test block display ofExample I and Example IV. The optical detail and intensity of themicrodefect structure of the two examples are clearly equivalent in FIG.1.

The equivalence of the optical sensitivity and clarity of the Examples1, 11 and Ill compositions to the much more concentrated composition ofExample IV, together with the LOX compatibility of Examples 1, II and111 and non-compatibility of Example IV, clearly establish the inventiveadvance of this invention over prior teachings in the dye penetrantinspection art.

Obviously many modifications can be made in this improvement in thesensitive dye penetrant compositions. it is therefore understood thatwithin the scope of the appended claims, the invention may be practicedotherwise than as specifically described.

1 claim:

1. A sensitive liquid dye penetrant for a metal surface which leaves aliquid oxygen (LOX) compatible defect indicating dye penetrant residueupon the surface and in any surface defects upon evaporation of thesolvent portion of the penetrant, comprising:

a. N-methyl-2-pyrrolidone in a concentration up to one volume percent;

b. a ketone whose boiling point is not more than 218C in a concentrationup to five volume percent; 1

c. a fluorescent dye in a concentration up to one volume percent andsoluble in said pyrrolidone;

d. a brightening agent for said fluorescent dye in a concentration up toone volume percent and being soluble in said pyrrolidone; and

e. the remainder constituting a halocarbon solvent,

said halocarbon solvent having a boiling temperature below 260 F. atatmospheric pressure and being nontoxic, non-flammable, resistant tohydrolysis, and a solvent for the aforesaid dye penetrant components,

said dye penetrant being rendered non-reactive to liquid oxygen uponevaporation of said solvent.

2. The sensitive liquid dye penetrant of claim 1 and further including anonionic wetting and spreading agent constituting not more than fivevolume percent of said dye penetrant.

3. The sensitive liquid dye penetrant of claim 1, wherein said ketone isisobutyl heptyl ketone.

4. The sensitive liquid dye penetrant of claim 1, wherein saidhalocarbon solvent is selected from the group consisting of:

l-bromo-l-difluoro-2-bromo-2-difluoro ethane,

l-dichloro-l-fluoro-2 ethane, l-dichloro-l-fluoro-2-dichloro-2-fluoroethane,

1,1,1 trichloro ethane,

trichloroethylene, and

tetrachloroethylene.

5. The sensitive liquid dye penetrant of claim 1, wherein said nonionicwetting and spreading agent is a nonyl phenyl polyethylene glycol.

6. The sensitive liquid dye penetrant of claim 1, wherein the volumeratio of halocarbon solvents to the sum of the other components is atleast 10:1.

a: a: a:

2. The sensitive liquid dye penetrant of claim 1 and further including anonionic wetting and spreading agent constituting not more than fivevolume percent of said dye penetrant.
 3. The sensitive liquid dyepenetrant of claim 1, wherein said ketone is isobutyl heptyl ketone. 4.The sensitive liquid dye penetrant of claim 1, wherein said halocarbonsolvent is selected from the group consisting of:1-bromo-1-difluoro-2-bromo-2-difluoro ethane, 1-dichloro-1-fluoro-2ethane, 1-dichloro-1-fluoro-2-dichloro-2-fluoro ethane, 1,1,1 trichloroethane, trichloroethylene, and tetrachloroethylene.
 5. The sensitiveliquid dye penetrant of claim 1, wherein said nonionic wetting andspreading agent is a nonyl phenyl polyethylene glycol.
 6. The sensitiveliquid dye penetrant of claim 1, wherein the volume ratio of halocarbonsolvents to the sum of the other components is at least 10:1.